title: Self-assembly of short linear chains to A- and B-type starch spherulites and their enzymatic digestibility.
abstract: A novel process combining enzymatic debranching, melting, and crystallization was developed to produce spherulites from short linear α-1,4-linked glucans (short-chain amylose, SCA) with controlled enzyme digestibility. SCA was obtained by completely debranching waxy maize starch at 50 °C and 25% solids in 0.01 M sodium acetate buffer. The mixture was then heated to 180 °C followed by cooling and crystallization to form well-developed spherulites. Multiple analytical techniques including light microscopy, scanning electron microscopy, differential scanning calorimetry, wide-angle X-ray diffraction, and synchrotron small-angle X-ray scattering (SAXS) covered over 5 orders of length scale and were applied to study the morphology and structure of the spherulites. Spherulites crystallized at low temperatures (4 and 25 °C) had a large size (5-10 μm), a B-type starch X-ray diffraction pattern, a lower melting temperature (70-110 °C), and a higher digestibility (Englyst method) compared to the spherulites crystallized at 50 °C, which had a small size (1-5 μm), an A-type diffraction pattern, a higher melting temperature (100-140 °C), and a lower digestibility. Intact spherulites along with small fragments were observed after digestion with a mixture of α-amyase and amyloglucosidase, indicating that digestion was not homogeneous and preferentially occurred in weak spherulites. A second exposure of the undigested residues to the amylases showed a similar digestive pattern as with the parent spherulites, suggesting that the spherulites were hydrolyzed by enzymes at essentially a constant digestion rate between 20 min and 3 h.
authors.affiliation: Department of Grain Science and Industry, Kansas State University , Manhattan, Kansas 66506 , United States.
authors.forename: Liming
authors.initials: L
authors.lastname: Cai
authors.forename: Yong-Cheng
authors.initials: YC
authors.lastname: Shi
mesh_terms: D000688:Amylose / Q000032:analysis*; D003460:Crystallization; D004063:Digestion; D007517:Isoamylase / Q000737:chemistry*; D015394:Molecular Structure; D013213:Starch / Q000737:chemistry*; D003313:Zea mays / Q000737:chemistry*
chemical_list: D013213:Starch; D000688:Amylose; D007517:Isoamylase